NMR-MAS probe head with integrated transport conduit for an MAS rotor

ABSTRACT

An NMR MAS probe head ( 1 ) has an MAS stator ( 7 ) with a base bearing ( 8 ) and a front bearing ( 75 ) for receiving a substance to be measured at a measurement position within an MAS rotor. The front bearing has an opening for inserting the MAS rotor into the space between the base bearing and the front bearing. The opening can be closed by a closing device that, in a loading state, opens and, in a measuring state, closes the opening by means of a movement that is transverse with respect to an axis (a) through the centers of the base bearing and the opening of the front bearing of the MAS stator. This enables automated loading and unloading of the MAS rotor in the space between the base bearing and the front bearing inside the MAS stator in a simple way.

This application claims Paris convention priority from DE 10 2013 201110.5 filed Jan. 24, 2013, the entire disclosure of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

The invention concerns a nuclear magnetic resonance (=NMR) magic-anglespinning (=MAS) probe head with an MAS stator disposed in a tube,wherein the MAS stator comprises a base bearing and a front bearing forreceiving a substance to be measured at a measurement position in anelongated, substantially circularly cylindrical MAS rotor, wherein thefront bearing has an opening (which can be closed by means of a closingdevice) for inserting an MAS rotor into the space between the basebearing and the front bearing.

A stator with a screwable closing device for installation in an NMR MASprobe head of the type stated in the introduction has been commerciallyavailable for some time, for example, from Prof. Ago Samoson, Universityof Technology, Tallinn, Estonia.

Nuclear magnetic resonance (=NMR) spectroscopy is a process forinstrumental analysis with which, in particular, the chemicalcomposition of measurement samples can be determined. Radio-frequency(RF) pulses are irradiated into the measurement sample, which is locatedin a strong, static magnetic field, and the electromagnetic reaction ofthe sample is measured.

To reduce spectral line broadening due to anisotropic interactions, itis known that an NMR sample can, during spectroscopic measurement, betilted and rotated at the so-called “magic angle” of approx. 54.74° withrespect to the static magnetic field (“MAS”=Magic Angle Spinning). Forthis purpose, the sample is filled into an MAS rotor. MAS rotors arecylindrical tubes open at one end, which are closed with a cap, whereinthe cap is provided with vane elements (“impellers”). The MAS rotor isdisposed in an MAS stator and the MAS rotor is made to rotate by gaspressure by means of the vane elements. The MAS rotor and MAS stator arecollectively termed an MAS turbine.

During the NMR measurement, the MAS turbine is disposed in an NMR MASprobe head. The probe head has a cylindrical shield tube (also called“tube” for short) and usually a base box. The tube containsradio-frequency (=RF) electronic components, in particular RF resonatorcoils, and the MAS turbine, wherein the MAS turbine is disposed in theregion of the tube end facing away from the base box. The probe head istypically inserted with its shield tube into the vertical roomtemperature bore of a superconducting magnet from below, thenpositioned, and held with hooks, supports, screws, or the like. The MASturbine is then in the precise magnetic center of the magnet.

To replace an NMR sample or an MAS rotor filled with a substance to bemeasured on simple probe heads, it is necessary to remove the probe headfrom the magnet, i.e. to extract the probe head from the roomtemperature bore. For this purpose, the user kneels under the magnet,releases the supports and cable connections, and catches the probe headwhen it slides out of the magnet. Due to the eddy currents induced inthe metal parts of the probe head, in particular in the shield tube, andthe intrinsic weight of the probe head, removing the probe head, orindeed re-inserting it into the magnet, can require considerableexertion. To ensure safety, manufacturers of probe heads prescribe thatthe probe head should be removed by two people together. The rotor canthen be replaced manually on the removed probe head. Re-shimming isusually necessary after the rotor has been replaced and the probe headtherefore repositioned in the magnet, making the overall procedure verytime-consuming.

DE 38 18 039 A1 discloses a rotatable sample magazine provided on theprobe head in the immediate vicinity of the MAS stator such that thesample in the MAS stator can be replaced multiple times by the action ofgas pressure without removing the probe head or the sample magazine fromthe interior of the magnet.

The technical poster of Shevgoor et al., discloses use of a lift systemfor MAS rotors. At the tube end of a probe head facing away from thebase box, a transport tube is connected that extends through the roomtemperature bore of a magnet upward out of the magnet. By means of gaspressure, an MAS rotor can be transported through the transport tubeinto the MAS stator of the probe head mounted in the magnet, and an MASrotor can also be transported out of the MAS stator upward out of theprobe head.

Because the transport tube is routed through the room temperature bore,both the room temperature bore as well as regions above the magnetcontain obstructive structures, which increases the complexity of theapparatus. Initial installation of the probe head is also rendered moredifficult by the transport tube. The transport tube also has to berouted through the wall of the shield tube to the MAS stator, whichmakes RF shielding of the sample during NMR measurement more difficult.

In many cases, measurement of the sample under defined, extremetemperature conditions, in particular at cryogenic temperatures (−196°C. or lower) is desired. The interior of the shield tube is temperaturecontrolled or cooled. In this case, the passage of the transport tubethrough the tube at the end farthest from the base box constitutes athermal bridge that makes it more difficult to comply with defined,extreme temperature conditions.

DE 10 2008 054 152 B3 proposes a probe head with a base box and a tubeattached to and protruding from the base box which permits a fast changebetween different MAS rotors while facilitating RF shielding andcompliance with defined, extreme temperature conditions, wherein the MASstator for receiving an MAS rotor is disposed inside the tube in theregion of the tube end facing away from the base box. A transport tubeis provided for pneumatically conveying an MAS rotor inside thetransport tube, which extends in the interior of the tube from the basebox to the MAS stator. However, in this conventional configuration, thefront bearing does not have an opening, like on a generic probe head ofthe type defined in the introduction, which can be closed by means of aclosing device for introducing an MAS rotor into the space between thebase bearing and front bearing, so that changing rotors in the closedprobe head is not possible. In particular, on MAS rotors withdiameters<1.3 mm, closure at both ends is necessary to stabilize therotation.

The generic probe head having the characteristics defined in theintroduction and the stator offered by Prof. Ago Samoson with ascrewable closing device cannot, for their part, be used with a rotorwithout having to remove the probe head from the magnet—with someeffort.

This invention, on the other hand, has the object of providing an NMRMAS probe head of the type defined in the introduction with stabilizedrotation with which a rotor change is possible without opening the probehead, and in which the probe head can remain in place in the magnetsystem.

SUMMARY OF THE INVENTION

This object is achieved with an NMR MAS probe head of the type stated inthe introduction, characterized in that a transport tube for conveyingan MAS rotor inside the transport tube is provided, wherein thistransport tube extends in the interior of the tube from the base box tothe MAS stator, and that the closing device can, by means of a movementthat is transverse with respect to an axis through the centers of thebase bearing and the opening of the front bearing of the MAS stator,clear the opening in a loading state and close it for a measuring state.

This makes automated changing of the rotor possible without taking theprobe head out of the magnet.

Because the transport tube extends in the interior of the tube (shieldtube), it is possible to constitute the tube to be closed in the regionaround the MAS turbine, that is, in the region of the free tube end(facing way from the base box). It is not necessary for the transporttube to pass through the wall of the tube.

The shielding effect of the usually metallic conductive, butnon-ferromagnetic tube can then be completely preserved. Moreover, it isnot necessary to tolerate a thermal bridge caused by the passage of atransport tube through the tube in the region of the end farthest fromthe base box.

Only the tube of the probe head projects into the room temperature bore;the end of the room temperature bore of the NMR magnet that is oppositethe probe head does not need to be covered. This simplifies thestructure of an NMR apparatus, in particular of an NMR spectrometer. Theentire sample change (rotor change) can be performed from one end of theNMR magnet only, namely from the end with the NMR probe head (typicallythe underside of the NMR magnet) via a pneumatic lift system.

The sample change can be automated; preferably, a semi-automatic samplechange (changed triggered manually but performed automatically aftermanual triggering) is set up.

In a highly preferred embodiment of the inventive probe head, theclosing device has a pneumatic actuator that can at least effect themovement to clear the opening in the loading state, thus enablingautomated loading.

Embodiments of the invention are also preferred in which a pneumaticsample changing system for feeding and removing an MAS rotor to the MASstator is provided, which also contributes to automation of themeasurement preparations.

Advantageous variants of this embodiment are characterized in that thetransport tube has a Y-junction device with a blind hole section forintermediate storage of an MAS rotor.

The main functions of the Y-junction device (reversal device) are,

-   -   to avoid tight curves in the transport tube while loading and        unloading the MAS rotor, and    -   to enable favorable orientations of the MAS rotors, in        particular, with upwardly oriented closing caps during transport        and support on the closed base end of the sample tube of the        rotor (farthest from the cap) in the MAS stator. By avoiding        tight curves, the space requirement for the transport tube can        be greatly reduced. With the Y-junction device, the transport        direction of the MAS rotor after intermediate storage in the        blind hole section can be reversed by approximately 180° in a        simple manner without having to negotiate a 180° curve. During        the reversal maneuver, the orientation (i.e. the cap-to-base end        sequence) of the rotor changes relative to the transport        direction. The reversal device permits, in particular, insertion        of the rotor, the latter's base level being inserted first, into        the stator, wherein the insertion opening of the stator faces        away from the base box end of the sample tube. The transport        tube is routed from the base box past the stator to the blind        hole section. A tube section leading to the MAS stator (or also        directly to the MAS stator) and the tube section leading past        the stator to the base box are both accessible from the blind        hole section (typically with no or only little curvature of the        transport tube). The blind hole section can, if necessary, also        provide a resilient buffer volume to avoid hard impact of the        rotor on the base of the blind hole section and to facilitate        immediate removal of the rotor from the blink hole section.

A variant of these embodiments is advantageous in which the blind holesection is constituted in a rocker which can be swiveled about a pivot.In this way, curvatures in the transport tube, and in particular in atube section leading to the MAS stator are reduced or completelyavoided. The swiveling of the blind hole section can be controlled bygas pressure; typically, there are two end positions of the rotatableblind hole section, one in which the MAS stator is accessible and one inwhich the tube section leading to the base box is accessible.

In an alternative embodiment, the Y-junction device contains a branch ofthe transport tube. This is an especially simple implementation of theY-junction device. Note that in the branch region, a widened crosssection (as compared with the outer dimensions of the MAS rotor or theremaining transport tube) of the transport tube is provided. In anadvantageous variant, one or more nozzles are provided in the region ofthe branch for pneumatic redirection of an MAS rotor. In this way, thetransport direction of the rotor can be especially well controlled.Alternatively, it is also possible to only direct the rotor usingtransport gas flows at the branching point inside the transport tube.

A variant of the above embodiments is also preferred in which thepneumatic actuator of the closing device can be operated with the samecompressed air supply as the pneumatic sample change system. This makesthe system more compact and lower-cost.

In an especially preferred embodiment, the probe head is constituted inthe region of the tube as a Dewar vessel. The tube is double-walled,with a vacuum between the walls; this facilitates temperature-controland cooling of the sample in the probe head for NMR measurement. Becauseof the closed design there are no unwanted thermal bridges.

An embodiment is also preferred in which the MAS stator is rotatablysupported for setting the MAS angle. The rotation of the stator in theprobe head can further facilitate insertion and removal of the MAS rotorin a confined space. Tight curves are thereby avoided. The rotation ofthe stator can, for insertion and removal, set an angle of the statorbearing axis relative to the longitudinal direction of the tube (whichregularly corresponds at least in a good approximation to the directionof the static magnetic field in the NMR magnet) that is smaller than themagic angle.

In one class of advantageous embodiments of the inventive probe head,the closing device comprises a gate valve that closes the opening towardthe transport tube in the measuring state of the MAS rotor and opens itin the loading state via a movement that is transverse with respect tothe longitudinal axis. This has the advantage that the device foropening and closing can be implemented simply.

An alternative class of embodiments of the invention is characterized inthat the closing device comprises a gate valve that closes the openingtoward the transport tube in the measuring state of the MAS rotor andopens it in the loading state by a movement on a curved trajectoryhaving one component that is transverse and one component that isparallel to the longitudinal axis. This enables the closure to engage inthe opening of the front bearing of the MAS stator.

In advantageous variants of this class of embodiments, the gate valve isguided on the curved trajectory by means of a guide contour on one ormore guide pins, permitting simple implementation of the device foropening and closing.

Both of the aforementioned classes of embodiments of the inventive probehead can be further developed so that the gate valve contains a pressureelement loaded by spring force, which causes the opening to close in themeasuring state of the MAS rotor. In this way, closure is possible inthe operating state in the closing position without external force.

An especially preferred variant of these embodiments is characterized inthat the pressure element is loaded by a compression spring made ofnon-magnetic material, preferably CuBe or spring bronze. In this way,the NMR signal is not adversely influenced by the materials of thecompression spring.

Further advantages result from the description and the drawing.Moreover, the features stated above and further below can be usedinventively singly or together in any combination. The embodiments shownand described are not intended to be an exhaustive list, rather areexamples to explain the invention.

The invention is shown in the drawing and is explained in more detailusing the example of the embodiments. The figures show:

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 a schematic cross-sectional view of an inventive NMR MAS probehead, with a Y-junction device with a branch;

FIG. 2 an enlarged view of the free end of the tube of the probe head ofFIG. 1;

FIG. 3 a a schematic view of an inventive probe head in the region ofthe free end of the tube, with a Y-junction device, comprising arotatably supported blind hole section (rocker) in a first position;

FIG. 3 b the free end of the tube of FIG. 3 a, in a second position ofthe rotatably supported blind hole section;

FIG. 4 an enlarged view of the base box region of the probe head of FIG.1;

FIG. 5 a schematic cross-sectional view of an inventive NMR apparatuswith an inventive probe head introduced from below into the roomtemperature bore of the magnet;

FIG. 6 a schematic cross-sectional view of an inventive NMR MAS probehead without Y-section device, for insertion from above into the roomtemperature bore of a magnet;

FIG. 7 a a detail section, in the ejection position, of an embodiment ofthe inventive probe head, in which the gate valve closes the openingtoward the transport tube in the measuring state of the MAS rotor andopens it in the loading state via a movement that is transverse withrespect to the longitudinal axis;

FIG. 7 b the sectional view of FIG. 7 a, but in the spinning position;

FIG. 8 a a detail section, in the ejection position, of an alternativeembodiment of the inventive probe head in which the gate valve in theloading state of the MAS rotor frees the opening to the transport tubevia a movement on a kidney-shaped guide curve having one component thatis transverse and one component that is parallel to the longitudinalaxis;

FIG. 8 b the sectional view of FIG. 8 a, but in the spinning position;and

FIG. 9 a schematic sectional view of a probe head according to prior artwith the characteristics defined in the introduction and with a frontbearing that can be screwed on and off by hand for inserting or removingthe rotor.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention concerns a new system for replacing MAS rotors in an MASNMR probe head, wherein the probe head can remain mounted in the magnetof an NMR spectrometer.

FIG. 1 shows an inventive NMR MAS probe head 1 in vertical section. Theprobe head 1 essentially comprises a tube 2, which is to be insertedinto the room temperature bore for an NMR measurement, and a base box 3.The tube 2 is attached to the base box 3 and projects perpendicularlyfrom the base box 3 (in this case). The base box 3 remains outside theroom temperature bore of the magnet. The probe head 1 as a whole istypically held or attached via the base box 3, in particular on themagnet or a substructure of the magnet.

In this embodiment, the tube 2 has a double wall (with an outer wall 4 aand an inner wall 4 b), between which a vacuum is provided, so that thetube 2 is also constituted as a Dewar vessel for thermal insulation fromthe (usually room temperature) environment. Any necessarytemperature-control tubes, which are not shown in any greater detail,extend in the tube 2 and in which (in this case) a coolant such asliquid nitrogen circulates to cool the interior of the tube 2, includingthe sample to be measured in an MAS rotor and NMR measuring electronics,in particular, RF resonators in the region surrounding the MAS rotor.Alternatively (or additionally), the transport gas flow in the transporttube 10 and/or other functional gas flows (see below) can also becooled, also ensuring good cooling in the interior of the tube 2 (iftube 2 is well insulated).

As least one wall 4 a, 4 b of the tube 2 is made of electrically highlyconductive, but non-ferromagnetic metal (for example, copper). Themetallic tube wall effects shielding of the tube interior from externalalternating electromagnetic fields; for that reason, the tube 2 is alsotermed a shield tube.

The tube 2 is closed at its free end 5 (at the top in FIG. 1) facingaway from the base box 3; in particular, it contains no feed-throughsfor gas or transport tubes. Accesses into the tube interior, forexample, for electrical, gas, and transport tubes are exclusivelyprovided in the region of the end 6 of the tube 2 that is nearer thebase box.

The tube 2 contains an MAS stator 7 in the region of its free end 5. Thestator 7 can hold an MAS rotor (not depicted in FIG. 1) at the magicangle (relative to the longitudinal direction of the tube 2, which isoriented parallel to the static magnetic field in measuring operation)and act as a bearing for rotation about the longitudinal axis of therotor. The front end of the stator 7 has a base bearing 8, on which therotor can rest in the stator 7 (supported by gravity). The base bearing8 has two nozzles (not shown in detail) which provide a bearing gas flowand an ejecting gas flow. The stator 7 also has a first lower radialbearing 9 a near to the base bearing 8 and a second, opposite upperradial bearing 9 b, in which an opening for routing through the rotor isformed. The base bearing 8 and the first radial bearing 9 a face thebase box 3, and the second radial bearing 9 b face away from the basebox 3. The magnetic center of the magnet configuration is located in thecenter between the first and the second radial bearing 9 a, 9 b duringan NMR measurement. The stator 7 has gas nozzles (not shown in greaterdetail) that blow onto an inserted rotor and thus make it rotate.

A transport tube 10 for MAS rotors also extends in the interior of thetube 2. A first section 10 a of the transport tube 10 leads from the end6 of the tube 2 that is nearer the base box past the stator 7 to aY-junction device 11. A second section 10 b of the transport tube 10leads from the Y-junction device 11 to the stator 7. The Y-junctiondevice 11 comprises a blind hole section 13 and a branch 12 of thetransport tube 10 (see also FIG. 2). The transport tube 10 is generallyconstituted by flexible tubes and/or rigid tubes and, in addition tostraight sections, can also have curved sections (curves), taking intoaccount the size of the MAS rotors and the play of the rotors in thetransport tube 10. The rotors are pneumatically conveyed in thetransport tube 10 by gas pressure and/or gravity.

The interior of the tube 2 also has a robust frame 14 on which thestator 7 and various electronic components (not shown separately) aredisposed for an NMR measurement on a measurement sample disposed in thestator. The first section 10 a of the transport tube 10 is constitutedin this case by a rigid tube, providing the frame 14 with betterstability. Some electronic components are attached directly to section10 a (not shown separately).

FIG. 2 describes the insertion of a MAS rotor 21 a, 21 b, 21 c into theMAS stator 7 of the probe head of FIG. 1 in detail. The representations21 a, 21 b, 21 c of the rotor show various stages during insertion.

A rotor 21 a is initially conveyed by a gas flow upward through thefirst section 10 a of the transport tube toward the Y-junction device11. The cap 22 of the rotor 21 a points upward at this stage. This cap22 has vane elements (impellers, not shown in FIG. 2).

Rotor 21 a is pushed from below upward into the blind hole section 13 bythe impinging gas flow. The gas flow then flows from section 10 athrough the branch 12 into the second section 10 b of the transport tubeto the stator 7. This gas flow then pulls the rotor 21 b toward thesecond section 10 b, i.e. the rotor 21 b swivels with its lower base endto the right and falls further. Finally, the rotor 21 c is pressed tothe right and downward by the gas flow toward the MAS stator 7 into thesecond section 10 b and into the stator 7. During this maneuver, thetransport direction undergoes a reversal (reversing maneuver).

A reverse gas flow is applied in order to eject a rotor 21 c from thestator 7. This initially presses the rotor 21 c from the stator 7through the second section 10 b into the blind hole section 13. A gasflow is then provided from the second section 10 b of the transport tubethrough the branch 12 into the first section 10 a of the transport tube.This pulls the rotor 21 b in the direction of the first section 10 a andfinally into the latter, so that the rotor 21 a is conveyed back throughthe first section 10 a of the transport tube to the base box. Here too,the transport direction undergoes a reversal (reversing maneuver).

Due to the Y-junction device 11, which, seen from the base box islocated beyond (behind) the MAS stator 7, a 180° curve in the transporttube can be replaced by the reversing maneuver, and at the same time,access to the MAS stator 7 from the side facing away from the base boxcan be provided through the second radial bearing 9 b (in FIG. 2 fromabove). Without the Y-junction device 11, the rotor would have to berouted around a tight curve of at least 180°−54.7°=125.3° to be conveyedfrom the vertical first section 10 a of the transport tube into thestator 7, tilted at the magic angle, and back again. Because the radiusof curvature of a transport tube is limited by the dimensions of therotor, such a tight curve would require a large amount of space in thetube of the probe head. By avoiding the tight curve, the tube can have asmall interior diameter ID so that an inventive probe head can beinserted into even narrow room temperature bores of magnetconfigurations. In the embodiment shown in FIG. 2, only a slight curveof 54.7° is provided in the region of the second section 10 b of thetransport tube. According to the invention, the outer diameter of thetube can easily be limited to 40 mm or 73 mm for usual room temperaturebores.

Note that during the entire conveying in and out action and during theNMR measurement, the cap-end of the rotor 21 a, 21 b, 21 c remainsessentially oriented upward so that there is no danger that samplematerial will spill or leak out if the cap is not tight.

To support the redirection of a rotor 21 b in the region of the branch12, a nozzle (or also a plurality of nozzles, in particular mutallyopposite nozzles) can be provided that can pneumatically deflect the MASrotor 21 b so that the rotor 21 b takes the desired path at the branch12.

Moreover, the MAS stator 7 can be swivelably supported to reduce thecurve in the movement of the MAS rotor 21 b, 21 c when conveying fromblind hole section 13 into the MAS stator 7 and vice versa. Forconveying, the MAS stator 7 would then be swiveled clockwise accordingto swivel direction S (in this example, shown for swiveling about themagnetic center); then the second section 10 b of the transport tubecould be steeper; the probe head could then be implemented even morecompactly. For the positions of the stator 7 for measuring the NMR tubeat the magic angle and for conveying the rotor, fixed stops areadvantageously provided; swiveling can be achieved by gas pressure.

FIG. 3 a shows an alternative embodiment of a Y-junction device 31 in aninventive NMR MAS probe head. Only the differences with respect to theembodiment of FIG. 2 are explained.

The Y-junction device 31 has a rotatably supported blind hole section32, which is constituted in a rocker 32 a; the rocker 32 a can beswiveled in a sector region 32 b about a pivot (here above). An MASrotor 21 a can be introduced into the blind hole section 32. In thefirst position of the rocker 32 a shown in FIG. 3 a, the blind holesection 32 is accessible from the first section 10 a of the transporttube, leading to the base box. In particular, a rotor 21 a can beconveyed (through the first section 10 a) into the rocker 32 a by a gasflow from below, or conveyed out by a gas flow from above (through thenozzle 33 at the end of the blind hole section 32) to the end of thetransport tube nearer the base box.

If an MAS rotor 21 a is completely inserted into the rocker 32 a, thelatter can be swiveled, in particular into the second position shown inFIG. 3 b. In this second position, the blind hole section 32 isaccessible for the second section 10 b of the transport tube or for thestator 7. If gas is blown into the blind hole section 32 through thenozzle 33, the rotor 21 b is conveyed into the stator 7. In the reversedirection, by blowing a gas flow from the base bearing 8, the rotor 21 bcan be conveyed into the rotatable blind hole section 32. In this way,the Y-junction device 31 will permits a space-saving reversing maneuver.

The rocker 32 a can be operated (swiveled) by a pneumatic actuator, notdepicted in further detail; the positions shown in FIGS. 3 a and 3 beach show end positions at a mechanical stop (edges of the sector range32 b).

In the embodiment of the tube of the probe head in FIGS. 3 a, 3 b, thetube only has a single wall 4.

FIG. 4 illustrates the base box 3 of the probe head of FIG. 1 in moredetail. The base box 3 comprises a support 40 for the tube 2 andelectrical connections as well as transport gas and functional gasconnections (usually bearing gas, driving gas, VT gas, insert gas,ejecting gas, purging gas and drying gas), not shown in further detail,and any necessary coolant connections. In the embodiment shown, a rotorgas lock 41 is also provide which, in this case, is constituted as acryo gas lock. The rotor gas lock 41 is in the extension of thetransport tube (of its section 10 a in this case) and has a loading andunloading station 42.

The loading and unloading station 42 has a lower opening that can beclosed with a rotor catcher 43. The rotor catcher 43 can hold an MASrotor and an MAS rotor can be conveyed out of and into the loading andunloading station 42 manually with it (for example, to change therotor). The loading and unloading station 42 has an access 44 for insertgas. Upon removal of the rotor catcher 43, the loading and unloadingstation 42 is automatically purged with outflowing eject gas. The rotorgate 41 has an enclosure 45, which has a thermally insulating effect andshields from room air in a gas-tight manner. The stator of the MASturbine is (directly and/or indirectly) accessible from the loading andunloading station 42.

The rotor gas lock 41 can comprise an additional stator into which anMAS rotor can be inserted and in which the MAS rotor can be made torotate by gas flow propulsion (not depicted). The region of the statorof the rotor gas lock 41 can be cooled (preferably with the same coolantor gas flow with which the interior of the tube 2 is also cooled) sothat sample material can be cooled in the interior of a rotor whilebeing rotated (“cooling turbine”). This ensures a rotationallysymmetrical distribution of the solidified sample material in the rotor.A rotor can be conveyed by gas pressure from the loading and unloadingstation 42 into the stator of the cooling turbine and, from there, afterthe rotor has been cooled and stopped, conveyed by gas pressure,(preferably directly) into the stator of the MAS turbine (“insert”). Ameasured rotor can (preferably directly) be ejected from the stator ofthe MAS turbine to the loading and unloading station 42 or into therotor catcher 43 (“eject”). Between the cooling turbine and verticaltransport tube (cf. section 10 a), the rotor gas lock 41 then has amechanical Y-junction (not depicted in detail) with three positions: Afirst position for the route rotor catcher—cooling turbine, a secondposition for the route cooling turbine—MAS turbine, and a third positionfor the route MAS turbine—rotor catcher.

The rotor gas lock 41 constituted as a cryogenic gas lock can, as shownin FIG. 4, be integrated into the base box 3 of the probe head, or beflanged onto the base box 3 (or also directly on the tube 2) (inparticular, detachable via a mechanical interface), or also be separatefrom the probe head and, for example, be located at the base below theNMR magnet, in which case a thermally insulating connection element withthe probe head should be used. It is also possible to provide only theloading and unloading station 42 separately from the probe head (forexample, on a laboratory bench), and to connect these to the rest of therotor gas lock 41 (which is then disposed on or in the probe head) and,in particular, directly to the stator of a cooling turbine via flexibleor rigid gas-pressure-operated transport tubes. To be operated, therotor gas lock 41 requires a supply unit, which provides or controls gasflow (including coolant flows) and electric switching operations. Thesupply unit can be integrated into the base box 3; however, the supplyunit is preferably separate from the base box 3 and far enough away fromthe probe head to preclude mutual interference, in particular with RFcomponents in the probe head.

The rotor gas lock 41 and/or the probe head can comprise:

-   -   Light barriers for determining the position of rotors;    -   Temperature sensors for determining the temperature of rotors,        in particular in the cooling turbine or the MAS turbine,    -   Valves for controlling gas flows, in particular transport gas        flows.

FIG. 5 shows an inventive modified NMR apparatus 51, comprising asuperconducting magnet configuration 52 (here comprisingsolenoid-shaped, superconducting magnet coils, not depicted in detail)with a vertical room temperature bore 53. The magnet configuration 52 issupported on robust supports 54. An inventive NMR MAS probe head 1 isinserted into the room temperature bore 53 (cf. FIG. 1). The largestpart of the tube 2 of the probe head 1 is inside the room temperaturebore 53, while the base box 3 of the probe head 1 is disposed outsidethe room temperature bore 53 below the magnet configuration 52. Thelargest (upper) part of the room temperature bore 53 remains free, andin particular, the space above the magnet configuration 52 does not needto be covered with a sample changing device. Sample changes (changingrotors) can be performed from below through the probe head 1.

FIG. 6 shows another embodiment of an inventive NMR MAS probe head 61.The probe head 61 is provided for suspended mounting in a magnetconfiguration, i.e. insertion of the tube 2 of the probe head 61 fromabove into a vertical room temperature bore of the magnet configuration.

In the interior of the tube 2, a transport tube 10 extends, in which anMAS rotor can be conveyed pneumatically (with gas pressure) from a rotorgas lock 41 in the region of the base box 3 to an MAS stator 62 in theregion of the free end 5 of the tube 2 and back again. In this MASstator 62, the base bearing 63 and the first radial bearing 64 a faceaway from the base box 3, and the second radial bearing 64 b, throughwhich an opening for inserting the rotor extends, faces toward the basebox 3. The base bearing 63 is therefore disposed in a lowered positionso that the rotor can be supported on the base bearing 63 by gravity.Throughout the actions of entry through the gas lock, NMR measurement,and exit through the gas lock, the rotor can remain substantially in thesame orientation, namely with its closing cap facing upward. Entry ofthe rotor through the gas lock is performed in a substantially uniformdownward movement (without a reversing maneuver), and also exit throughthe gas lock is performed in a substantially uniform upward movement(without a reversing maneuver).

Note that the magnetic center is typically somewhat below the geometriccenter of a magnet configuration and therefore the tube 2 in theembodiment depicted in FIG. 6 may have to be comparatively longer thanin the embodiment shown in FIG. 1.

The schematic detail sections of FIGS. 7 a and 7 b, show an embodimentof the inventive NMR MAS probe head, in which the closing device 76 acomprises a gate valve 77, which, in the measuring state of the MASrotor 21 a-21 c, closes the opening 76 b toward the transport tube 10and, in the loading state, opens it by a movement that is transversewith respect to the longitudinal axis.

Specifically, FIG. 7 a shows the gate valve 77 in its eject or loadingposition, while FIG. 7 b shows the corresponding spinning position, inwhich the NMR MAS measurement is performed. In this spinning position asshown in FIG. 7 b, the gate valve 77 is moved to the left, usually byapplication of pressure from the right-hand side, which is executed bymeans of a pressure element 79 (shown only very schematically in thedrawing) and usually loaded with spring force so that, instead of theopening 76 b, the front bearing 75 is positioned on the longitudinalaxis a as an extension of the transport tube 10 and therefore closes thespace inside the MAS stator 7 between the base bearing 8 and the frontbearing 75 toward the transport tube 10 in the measuring state. Theoutlet air cross-section of the pressure element 79 for controlling theactuator can be set with a set screw (also not shown in detail).

FIGS. 8 a and 8 b show an alternative embodiment of the inventive NMRMAS probe head in which the closing device 86 a, in turn, comprises agate valve 87, which, in the measuring state of the MAS rotor 21 a-21 c,closes the opening 86 b toward the transport tube 10, but opens it inthe loading state, not by a linear movement that is transverse withrespect to the longitudinal axis a, but by a movement along akidney-shaped curve having one component that is transverse and onecomponent that is parallel to the longitudinal axis a. For this purpose,the gate valve 87 is guided on the curved trajectory by means of guidecontours 88, 88′ on guide pins 88 a, 88 a′.

Specifically, FIG. 8 a shows the gate valve 87 in its eject or loadingposition, in which the rotor channel is free. In this position (shownvery schematically in the drawing), compressed gas is applied to thepneumatic cylinder of a spring-loaded pressure element 89. Bycomparison, FIG. 8 b shows the corresponding spinning position, in whichthe NMR MAS measurement is performed. In this spinning position, thepneumatic cylinder is not under pressure. The gate valve 87 is pressedby the application of spring force from the bottom right to the top leftso that, instead of the opening 86 b, the front bearing 85 is positionedon the longitudinal axis a as an extension of the transport tube 10 andthe space inside the MAS stator 7 between the base bearing 8 and thefront bearing 85 closes toward the transport tube 10 in the measuringstate.

Here too, the outlet air cross-section of the pressure element 89 forcontrolling the actuator can be set with a set screw (also not shown indetail).

The pressure elements 79; 89 are usually loaded by a compression springmade of non-magnetic material, preferably CuBe or spring bronze.

FIG. 9 shows a schematic detailed section of a generic probe headaccording to prior art, which has the characteristics defined in theintroduction and comprises a front bearing 95 that can be screwed on andoff by hand for inserting or removing the rotor in the space inside theMAS stator 7 between base bearing 8 and front bearing 95. When the frontbearing 95 is screwed on, the opening 96 b of the closing device 96 a isalways closed so that automated loading and unloading with the rotor isnot possible. This must always be inserted and removed by hand.

We claim:
 1. A nuclear magnetic resonance (=NMR) magic-angle spinning(=MAS) probe head for measuring a substance at a measuring position, theprobe head comprising: a tube; an elongated, substantially circularlycylindrical MAS rotor, said MAS rotor structured for receiving thesubstance to be measured; an MAS stator disposed in said tube, whereinsaid MAS stator has a base bearing and a front bearing having anopening, said MAS stator being structured for receiving said MAS rotorfollowing insertion thereof into said MAS stator through said openingand into a space between said base bearing and said front bearing,wherein said MAS stator has an axis passing through a center of saidbase bearing and a center of said opening; a transport tube forconveying said MAS rotor inside said transport tube, said transport tubeextending in an interior of said tube to said MAS stator; and a closingdevice, said closing device structured, in a loading state, to open and,in a measuring state, to close said opening in said MAS stator by meansof a movement that is transverse with respect to said axis of said MASstator.
 2. The probe head of claim 1, wherein said closing device has apneumatic actuator structured to open said opening in said loadingstate.
 3. The probe head of claim 2, further comprising a pneumaticsample changing system for feeding and removing said MAS rotor to andfrom said MAS stator.
 4. The probe head of claim 3, wherein saidtransport tube has a Y-junction device with a blind hole section forintermediate storage of said MAS rotor.
 5. The probe head of claim 4,wherein said blind hole section is constituted in a rocker and saidrocker is structured to swivel about a pivot.
 6. The probe head of claim3, wherein said pneumatic actuator of said closing device is operatedwith a same compressed air supply as said pneumatic sample changingsystem.
 7. The probe head of claim 1, wherein the probe head isconstituted as a Dewar vessel in a region of said tube.
 8. The probehead of claim 1, wherein said MAS stator is rotatably supported forsetting an MAS angle.
 9. The probe head of claim 1, wherein said closingdevice comprises a gate valve, which, in said measuring state of the MASrotor, closes said opening with respect to said transport tube and, insaid loading state, releases said opening via a movement that istransverse with respect to said longitudinal axis.
 10. The probe head ofclaim 1, wherein said closing device comprises a gate valve, which, insaid measuring state of said MAS rotor, closes said opening with respectto said transport tube and, in said loading state, releases said openingvia a movement along a curved trajectory having one component that istransverse and one component that is parallel to said longitudinal axis.11. The probe head of claim 10, wherein said gate valve is guided alongsaid curved trajectory on one or more guide pins by means of a guidecontour.
 12. The probe head of claim 9, wherein said gate valve containsa pressure element loaded with spring force, which, in said measuringstate of the MAS rotor, effects closure of said opening.
 13. The probehead of claim 12, wherein said pressure element is loaded by acompression spring made of non-magnetic material, of CuBe or of springbronze.